Known in the art is a method for preparing difurfurylideneacetone oligomer under laboratory conditions. It comprises heating of difurfurylideneacetone in the presence of acid catalysts such as benzenesulphonic acid, metal chlorides at a temperature within the range of from 70.degree. to 120.degree. C. or without any catalyst at a temperature above 180.degree. C. (cf. Plasticheskije massy, No. 12, 1960, p. 9-13, and No. 2 of the same Journal, 1974, p. 77). The process of oligomerization in the presence of said catalysts proceeds at a high rate thus hindering the process control and preparation of the desired products with the predetermined characteristics. Without catalysts the oligomerization process occurs at high temperatures and features a long duration (above 10 hours).
Known in the art is a method for preparing difurfurylideneacetone oligomer implemented on a pilot-plant scale. The method comprises charging difurfurylideneacetone in the form of a powder-like product containing no moisture into a reactor, melting at a temperature of 60.degree.-65.degree. C., heating at a temperature ranging from 120.degree. to 130.degree. C., followed by distilling-off low-molecular compounds, whereafter heating of the reaction mass is continued to a temperature within the range of from 200.degree. to 210.degree. C. with residence of the reaction mass at this temperature for a period of from 60 to 90 minutes until the oligomer is formed. The final oligomer is drained into pans and cooled to the ambient temperature.
This prior art method has certain disadvantages hampering its realization on a commercial scale, namely:
1. The process duration on the whole is 8-10 hours.
2. Carrying out oligomerization at a high temperature makes the process difficult to control due to the risk of a sharp elevation of temperature because of the exothermal character of the oligomerization reaction and outburst of the reaction mass out of the reactor. All this hinders the determination of the moment of the process completion and results in that different lots of the oligomer considerably differ from each other in their properties, i.e. the final desired product is unstable in respect of its characteristics.
3. Distilling-off low-molecular compounds from the dry difurfurylideneactone at a temperature of from 120.degree. to 130.degree. C. results in a sharp foaming of the reaction mass which is often accompanied by its outburst from the reactor.
4. Charging of the dry powder-like difurfurylideneacetone into the reactor is frequently accompanied by the formation of its aerosol which substantially impairs sanitary and hygienic conditions of labour.
5. Preparation of the dry monomer necessitates the stage of drying with the use of special drying unit. This complicates the process for the production of the oligomer and adds to its production costs.
Also known in the art is a method for the production of difurfurylideneacetone oligomer which consists in that the starting difurfurylideneacetone with a moisture content of from 150 to 40% is charged into a reactor and heated to a temperature of from 60.degree. to 70.degree. C. for melting. The molten furfurylideneacetone is heated at a temperature of from 80.degree. to 90.degree. C. under progressively increasing vacuum to 180-200 mm Hg. Then a catalyst is added, i.e. orthophosphoric acid in an amount of from 0.8 to 1.2% as calculated for the dry difurfurylideneacetone. The resulting reaction mass is heated to a temperature of 160.degree.-165.degree. C., followed by residence thereof at this temperature for a period of from 40 to 70 minutes, whereupon oligomerization of difurfurylideneacetone occurs.
This method for the production of difurfurylideneacetone oligomer is commercially realized; however, at the final stage the process of oligomerization of difurfurylideneacetone in the presence of an acid catalyst occurs but with a very high speed which hinders the possibility of determination of the degree of readiness of the oligomer. If the process is abruptly stopped (the reaction mass is sharply cooled) somewhat earlier, then an oligomer is obtained which has a low dropping point (75.degree.-90.degree. C.) hindering its processing.
If the process of oligomerization with an acid catalyst is not stopped at the stage of the oligomer readiness, then there occurs an uncontrollable reaction of polymerization of difurfurylideneacetone accompanied by a sharp elevation of temperature up to 200.degree.-300.degree. C. The resulting non-fusible and insoluble polymer is not suitable for any further processing.
The oligomer with the required properties has a life time of several minutes only (5-15 minutes), during which period it is impossible to determine its dropping point due to a long time required for the analysis. For this reason, the degree of readiness of the oligomer is defined by the increase in its brittleness in the cooled state by touch when continuously taking-off samples. In practical realization of this method, the quality of the obtained oligomer completely depends on the skill and experience of a person carrying out the synthesis of the oligomer of difurfurylideneacetone. By this method it is possible to obtain the oligomer with the maximum dropping point of 130.degree.-140.degree. C. This oligomer, when mixed with graphite in the manufacture of graphitized plastics, should be subjected to rolling for a period of 5 to 8 minutes. The modern processes for the manufacture of graphitized plastics contemplate a single passing of the material through rolls, i.e. rolling should be effected within several seconds. These requirements are met by oligomers with a dropping point within the range of from 150.degree. to 170.degree. C.